Cathode ray tube



g- 19, 1941- B. c. FLEMING-WILLIAMS ,744

CATHUDFJ RAY TUBE Filed Oct. 28, 1938 Patented Aug. 19, 1941 CATHODE RAYTUBE Brian Clifford Fleming-Williams, Cranfo'rd,

England Application October 28, 1938, Serial No. 237,545

In Great Britain November 3, 1937 10 Claims.

This invention relates to cathode ray tubes.

A feature of the invention is the provision of a cathode ray tubewherein the beam is divided into two parts which are independentlydeflectable in one direction.

An arrangement according to the invention may be used, if means are alsoprovided to deflect both parts of the beam together in the perpendiculardirection, for the purpose of obtaining 'two traces simultaneously on afluorescent screen, representing the variations of two differentphenomena with respect to a single variable. A simple example is therepresentation of the variations of a voltage and of a correspondingcurrent with respect to time.

If one part of the beam only is deflected in the direction ofindependent deflection, then the other part may be employed to trace anaxis of abscissae for the curve traced by the first part of the beam.

According to the invention there is provided a hard vacuum cathode raytube having an electron gun and having a pair of electrostatic deflectorplates arranged to provide the first or the only deflection of theelectron beam issuing from said gun, characterised in that an additionalplate electrode is positioned in the space between said deflector plateswith its plane perpendicular to the plane of the deflection produced bysaid deflector plates and parallel to the axis of the undeflectedelectron beam, and so that it cuts through the path of the electron beamwhich will therefore pass partly on one side and partly on the otherside of said additional plate, and further characterised in that saidadditional electrode is arranged to be maintained at the same potentialas the final anode of the gun, whereby the electrostatic deflectionfield produced between said additional electrode and one of saiddeflector plates by a potential difierence between them will be renderedsubstantially independent of the potential difference between saidadditional electrode and the other of said deflector plates.

By the term hard vacuum cathode ray tube in this specification is meanta cathode ray tube in which the electron beam is mainly iocussed byelectron lenses.

It will be understood that in the above statement. of the invention theexpression the first or the only deflection is not intended to excludethe possibility of a small deflection ap plied in the gun orin theregion between the flection may be provided, for example, by magneticmeans in order to compensate for inaccuracy of alignment of theadditional electrode and the gun, or to obtain a desired distribution ofcurrent between the two parts of the beam where widely diiierent writingspeeds are to, be employed for the two parts. The expression is,however, intended to exclude any means for providing deflection throughangles comparable with the maximum useful angles of deflectionobtainable with the deflector plates.

It is desirable that the deflection system should be as near as possibleto the gun so that it will operate upon the beam where this is as wideas possible. In this way, loss of current to the additional plate isminimized.

In the accompanying drawing, Figure l is a diagrammatic elevation, shownpartly in section, of the electron gun and deflector plates of a highvacuum cathode ray tube according to the invention. Figure 2 is anexploded perspective View of the deflector plates and associated partsof the structure shown in Figure 1.

In Figure 1, the parts I, 2, 3 and 4 indicate diagrammatically anelectron gun having the cathode (unseen) within the modulating electrodel, theelectron beam being emitted vertically therefrom throughcylindrical first and second anodes Z and 3 (which will also have discportions which are unseen) and then through the third (final) anode 4which is shown in section. The disc part 4a of this final anode acts asa mask and collects all electrons from the beam which are notconcentrated into the aperture 4b.

The electron beam issues upward from the aperture 4b as a slightlyconvergent pencil. It then passes between th deflector plates 5 and 8which are arranged symmetrically and sufficiently far apart to beoutside the path of the beam. The additional plate electrode 1 ispositioned in th plane which contains the axis of the electron gun (thecenter line of the beam) and which is perpendicular to the plane of thedeflection caused by electrostatic fields due to deflecting potentialson plates 5 and 6.

The electron beam is of such width at this part of the tube that only asmall portion of the electron current is collected by the plate I whenthis is maintained at the potential of the final anode 4 of the gun. Thepart of the beam which passes between plates 5 and l is screened by theplate I from the deflecting influence of plate 5.

gun and the deflector plates. Such a small (16- il y, the P Of the be mw ich passes between plates 6 and 1 is screened from plate 5. Adeflecting potential applied between plate 1 and either deflector plate5 or 6 will produce a deflection only in that part of the beam whichpasses between that deflector plate and plate 1. It is found that ifplate I is not unduly long, as measured along the axis of the tube, thenthe parts of the beam may be deflected not only in the directions awayfrom plate 1 but also in the directions towards plate 1 without seriousloss of current plate I. When no deflecting potentials are applied, thetwo parts of the beam will focus in a single spot on the screen.

With practicable dimensions of plate I, it is found that the screeningof each part of the beam from the opposite deflector plate is not quiteadequate for some purposes. fore, preferred that small additionaldeflector electrodes be provided to compensate for the resulting errors.Such electrodes are shown as wires 8 and 9 which are connected to thedeflector plates Band 6 respectively. An alternative method ofeliminating these errors is to' provide the necessary degree of couplingbetween the external circuits connected to thedeflector plates 5 and 6.Thepreferred method of mounting the plates 5, 5' and 1 will be 'betterseen from Figure 2. Annular discs'of mica ill and H have central holesslightly smaller in diameter than the width the slits lea, lilo, thedisc H is superposed and the plate l is fitted through the slits Hb lb.The discs lfl and It are secured closely together by eyelets through anumber of holes lild, Hd. In this way the flangesFaa, 6a are held in theplanes of theadjacent faces of these mica discs, and theinclination ofthese plates to the axis is thus fixed. The plate I is held in the planecontaining the axis by Welding the lugs la to memberl2, which is ametallic plate having a, central aperture slightly smaller than theapertures in discs iii and II and having ears iia which, on assembly,are bent around the edges of, and on to the lower face of, disc It. Themember i2 is also provided with lugs i217 which are somewhat springy andare arranged to press against a conductive coating on the envelope ofthe tube. The connection of plate 1 to the final anode of the gun mayconveniently be made by a wire from one of these lugs [21) to the finalanode 4 but this connection is shown merely diagrammatically, as alsoare the connections of wires 8 and 9 to the deflector plates 5 and 6.

The ears lid and lugs l2b are omitted from Figure 1, in order to renderthat figure more clear.

The wires 8 and 9 may be supported by welding to longitudinal supportwires parallel to the axis passing through holes lild, lid, and throughsimilar holes in micas which support the parts of the gun.

With a diameter of the aperture ib in the final It is, there-.

sions of the deflector plate assembly have been found satisfactory:

Millimeters Length of deflector plates (as seen in Figure 1) 6 Length ofplate 7 (as seen in Figure l) 7.5

.Spacing of inner face of each deflector plate from axis:

of each deflector wire (centre) from 5.2 Spacing of each deflector wire(centre) top face of member E2 What I claim is:

l. A cathode ray, tube comprising an electron gun for emitting anelectron beam, electrode means for controlling the convergency of saidbeam, means comprising a plate electrode for dividing said beam into aplurality of parts, means comprising a pair of electrostatic deflectorplates co-operating with said second mentioned means for independentlydeflecting each of said parts and means comprising a pair of additionaldeflector elements each connected to opposite former mentionedelectrostatic deflector plates for controlling the deflection. of saidparts.

2. A cathode ray tube comprising an electron gun having an anode foremittingan electron beam, means for controlling the convergency of theelectron beam to focus the electrons on a single spot on the screen, apair of electrostatic deflector plates each of which is independentlyenergized positioned to deflect the electron beam issuing iromsaid gun,a plate electrode connectedto said anode of said electron gun, saidplate electrode being positioned between the electrostatic deflectorplates in the path of the electron beam whereby the electron beam uponpassing the deflector plates and plate electrode is divided into twoparts each of which passes onseparate sides of said plate electrode andare independently deflected by the electrostatic deflection fieldsexisting between the plate electrode and each of the electrostaticdeflector plates.

3; A, cathode ray tube comprising an electron gun having a plurality ofanodes for emitting an electron beam, means for controlling theconvergency of theelectron beam to focus the electrons on a single spoton the screen, a pair of independently energized electrostatic deflectorplates positioned on each side of the beam, a plate electrode connectedto the last anode of the'electron gun, said plate electrode being posi-1 beam, said plate electrode also being positioned anodeioi' 3 mm,the'following leading dimenso that it. cuts ,the path of. the electronbeam which will therefore pass partly on one side and partly on theother side of theplate electrodes whereby each of the parts will beindependently deflected by the electrostatic deflection fields existingbetween the plate electrode and each of the independent electrostaticdeflector plates.

4. A cathode ray tube comprising an electron gun having a plurality ofanodes, a pair of electrostatic deflector plates positioned one on eachside of the beam and arranged to deflect the electron beam issuing fromsaid gun, a plate electrode connected to one of said anodes of theelectron gun, said plate electrode being positioned between saidelectrostatic deflector plates with its plane substantiallyperpendicular to the plane of the deflection of the electron beamproduced by said electrostatic deflector plates and parallel to the axisof the undeflected beam, said plate electrode also being positioned sothat it cuts through the path of the electron beam which will thereforepass partly on one side and partly on the other side of the plateelectrode, a pair of deflector electrodes arranged one on each side ofthe beam, means for connecting each deflector plate with a deflectorelectrode, positioned at the opposite side of the beam, said deflectorelectrodes being so positioned as substantially to compensatefor anydeflection sensitivity of the part of the beam on the same side as thedeflector electrode with respect to variations of potential differencebetween the deflector plate and the oppositely positioned deflectorelectrode.

5. In a cathode ray tube comprising an electron gun, a pair of deflectorplates and a plate electrode positioned between said deflector plates,supporting structure for said plates for positioning them adjacent theaxis of the electron gun comprising in combination a disc of insulatingmaterial provided with an opening therein, a plurality of slots inaligned position in opposite sides of the opening of said disc, saidslots being adapted to receive said elements and hold them inpositiontransverse of the said central opening.

6. In a cathode ray tube comprising. an electron gun, a pair ofdeflector plates and a plate electrode positioned between said deflectorplates, supporting structure for said plates for position ing themadjacent the axis of the electron gun, comprising in combination aplurality of superimposed annular discs of insulating materialcontaining aligned slots on opposite sides of the central opening forreceiving said plates, flanges on said deflector plates positionedbetween said superimposed discs for maintaining said deflector plates inposition, a plurality of lugs on said plate electrode, and meanscomprising an apertured member secured on said superimposed annulardiscs co-operating with said lugs for maintaining said plate electrodein place between said deflector plates.

'7. In a cathode ray tube comprising an electron gun, a pair ofdeflector plates and a plate electrode positioned between said deflectorplates, supporting structure for said plates for positioning them inalignment with the electron beam from the electron gun, comprising incombination a disc of insulating material provided with an openingtherein containing aligned slots on opposite sides of the openingadapted to receive said deflector plates and plate electrode, a seconddisc of insulating material provided with an opening thereinsuperimposed on said disc for maintaining said deflector plates inposition, aligned slots on opposite sides of the opening of said secondannular disc for receiving said plate electrode and means comprising anapertured member superimposed on said second annular disc for securingsaid p ate electrode in place.

8. A cathode ray tube comprising an electron gun for emitting anelectron beam, means for controlling the convergency of said beam tofocus the electrons on a single spot on the screen, means comprising aplate electrode located in the path of the beam for dividing theelectron beam into a plurality of parts and means comprising a pair ofindependently energized electrostatic deflector plates each of which ispositioned on opposite sides of said plate electrode for producingelectrostatic deflection fields for deflecting each of said beam parts,said electrostatic deflection field for each beam part being independentof the energization of the deflection field of the other beam part.

9. In a cathode ray tube comprising an electron gun for emitting anelectron beam, means for controlling the convergency of said beam tofocus the electrons on a single spot on the screen, a pair of spacedelectrostatic deflector plates between which said electron beam passes,a plate electrode symmetrically positioned intermediate said pair ofspaced electrostatic deflector plates with its plane parallel to theaxis of the electron beam so that the electron beam is divided into twoparts by said plate electrode, means for separately energizing each ofthe said spaced electrostatic deflector plates to produce independentelectrostatic deflection fields between the plate electrode and each ofthe spaced electrostatic deflector plates whereby each of theaforementioned parts of the electron beam are independently deflected ina plane perpendicular to the axis of the plate electrode by theindependent electrostatic deflection fields existing between the plateelectrode and each of said spaced electrostatic deflection plates.

10. In a cathode ray tube comprising an electron gun for emitting an,electron beam, means for controlling theiconvergency of said beam tofocus the electron on a single spot on the screen, a pair of spacedelectrostatic deflector plates between which said electron beam passes,an electrode comprising a plate positioned intermediate said pair ofspaced electrostatic deflector plates with its plane parallel to theaxis of the electron beam, means for producing independent electrostaticdeflection fields between said electrode and each of said electrostaticdeflector plates whereby said electrode divides the electron beam intotwo parts and serves to shield each of said beam parts from theinfluence of the electrostatic deflection field located between the saidplate electrode and the electrostatic deflector plate positioned on theopposite side of the plate electrode from each of the bean parts.

BRIAN CLIFFORD FLEMING-WILLIAMS.

